Chlamydia trachomatis is the most prevalent sexually transmitted bacterial infection. Devastating reproductive consequences of chronic C. trachomatis disease and a predisposition to HIV infection make progress towards the development of effective vaccination strategies imperative. However, limited information in several key areas has severely hampered progress in this area. Animal models have shown that T cell responses are central to host resistance but do not reproduce all the critical features of human disease. C. trachomatis is an obligate intracellular pathogen that primarily infects columnar epithelial cells of the endocervix in women, yet little is known either of the inductive or effector phases of local immunity in these tissues. Immune cells at mucosal sites are phenotypically and functionally distinct from their counterparts in the circulation and it is increasingly clear that the local milieu plays an important role in regulating local immunity. Nevertheless, almost all human studies to date have focused, perhaps inappropriately, on C. trachomatis-specific immunity in the circulation, since great difficulties have, to date, attended isolation of endocervical lymphoid ceils. Here, each of these issues will be addressed. The primary focus of this application is to characterize T cell immune responses at the primary site of C. trachomatis infection in the human endocervix with the underlying hypothesis that activity of these subpopulations, rather than circulating T cells, most accurately reflects the critical host response against this pathogen. Initially, the local immune milieu will be characterized using secretions and cytobrush cell specimens from C. trachomatis-infected women both pre-and post-antibiotic treatment and from uninfected controls. Comparisons with circulating T cell populations will clarify unique features of the mucosal T cell repertoire. Next, the frequencies, cytokine expression profiles and lytic activities of endocervical and circulating C. trachomatis-specific CD4 and CD8 T cells both will be more closely defined both directly ex vivo and in cloned cell populations. Finally, in studies with our T cell clones, processing and presentation of C. trachomatis antigens will be characterized, using immortalized endocervical columnar epithelial cells that are genetically or biochemically manipulated for directed inhibition of specific intraceUular trafficking pathways. This study design will clarify interactions between C. trachomatis and the cervical immune system that will ultimately aid greatly in delineating protective immune responses against C. trachomatis and the development of effective vaccines.